The invention is based on a shutoff apparatus or safety means for preventing excess revolutions in fuel injection pumps as defined hereinafter. A safety means to prevent such overspeeding in injection pumps in internal combustion engines is known from DE-AS 19 13 808. In this apparatus, the high-pressure chamber is defined on one end by the pump piston, which executes the conventional stroke comprising reciprocating and rotational movements, and on the other end by the closing body of a safety valve, which is magnetically actuatable. Supplying an appropriate current to the coil of the electromagnet keeps the safety valve closed; the valve is opened whenever an exciting current for the electromagnet is attained such that threshold safety means in the control circuit of the electromagnet respond and break the current circuit. The exciter current attained at this instant corresponds to the maximum permissible rpm. In this known safety means for preventing excess rotation, the disadvantage is that the safety valve is exposed directly to the injection pressure, and the dropping of the electromagnet is not capable of automatically effecting an immediate opening of the safety valve. This opening is effected by a separate spring, which responds as soon as the injection pressure has dropped in the high-pressure portion of the pump.
A fuel injection pump is also known from German Design Pat. No. 1,890,843, in which the pump piston executing the reciprocating movements is surrounded in its upper portion by a cylindrical slide which has a relief bore leading to a return-flow line. The relief bore is opened at a predetermined instant during the compression stroke executed by the pump piston; the pressure in the pump work chamber or high-pressure chamber thereupon drops, because the fuel continuing to be displaced is capable of flowing back to the tank. The cylindrical slide is pressed by a prestressing spring against an upper stop and communicates at its other end, via a bore, with the portion of the inlet conduit located ahead of the throttle slide. When the inlet pressures are very high, the result in this case is that the pump work chamber is opened earlier.
There is a need for an electric shutoff apparatus for a distributor injection pump in internal combustion engines, especially 8-cylinder engines, which is not overly sensitive and which necessitates only small magnetic forces.